This invention relates to inverters in general and more particularly to a system for starting a shut down inverter.
Inverters for alternating standby and load operation which comprise a power section with controlled main valves and a control arrangement with a control unit for forming firing pulses, and with which a monitoring device for a single or three phase system for forming a start command is associated are used, for instance, in protected power supply systems or for strengthening weak systems or for supplying converter drives.
In protected power supply systems, the inverter can either be operated continuously and uninterrupted, or switched between standby and load operation. In a completely interruption free power supply, the load is supplied continuously by an inverter maintained in continuous operation, which is connected to a single or three phase system via a battery and a charging rectifier. In the event of a system failure, the power supply continues without interruption. The rectifier must be designed for simultaneously charging the battery and supplying the inverter. Because the energy is continuously transformed twice, the efficiency of such interruption free power supplies is unsatisfactory.
In other known protected power supplies, the load is supplied from the system network in normal operation. In the event of a system failure, an inverter is switched to delivering power and the load is switched to the inverter. The charging equipment need be designed only for the charging of the battery. Since no energy transformation takes place in normal operation, the losses are substantially lower than in an immediately ready standby system with a continuously operating inverter. The losses still occurring in normal operation depend on which type of standby operation is chosen for the inverter.
The inverter can be operated "no-load" during standby. Then, its control arrangement is in full operation. The controlled semiconductor valves of the inverter are addressed by firing pulses. The usual commutating processes take place. However, the output voltage of the inverter is disconnected. Due to the commutating processes, losses and noise occur continuously in the power section of the inverter, particularly in transformers and chokes. Further losses accrue in the information processing in the control unit and in generating the firing pulses.
Inverters are also known in which only the control unit is in operation during standby and generates firing control signals. However, the transmission of the firing control signals to the semiconductor valves of the inverter is blocked. Upon a start command, the firing control signals are connected through to the semiconductor valves. No commutation losses accrue in standby operation. The losses due to the continuously operating control unit are small. They can be reduced further if the firing control signals are blocked in standby operation ahead of the pulse output stages of the control unit. Then, only the information processing section in the control unit operates during standby.